Mixing amplifier



ATTORNEY.

uumnom mz m mnzm m. m 292 552 4 J 913 Q Q .Q\ v Q Hanna 5535mm "mam/ Patented July 26, 1938 UNITED STATES PATENT OFFICE tion of Delaware Application June 19,

2 Claims.

This invention pertains in general to radio circuits and specifically relates to a circuit for combining signalling energy of different frequencies.

The principal object of the invention consists in providing an electron tube circuit for combining different signalling energy frequencies supplied from different sources without interaction between the sources for producing an'output current which is the algebraic addition of the plural input currents.

A further object comprises providing a system for combining. modulated high frequency energy from which the carrier frequency has been eliminated, with a replacement carrier frequency to reproduce desired signals.

A further object consists in producing a mixing amplifier circuit for amplifying and combining one frequency with another in an electron tube to produce a combined amplified output.

These and other objects will be apparent from the following, reference being had to the accompanying drawing which is a diagrammatic illustration of a preferred embodiment of the invention.

The invention contemplates the provision of a system such as a wired radio receiving organization which receives modulated high frequency energy comprising modulation side band energy with the carrier frequency substantially eliminated. A separate and distinct carrier frequency is supplied at the point of reception to be combined with the modulation side band energy for replacement purposes to reproduce the original signal. In accordance with the invention, the

modulation side band energy and the independent replacement carrier frequency are combined in a mixing amplifier circuit to produce an algebraic addition of the two frequencies in a linear amplification process without inter-action between the two sources of frequencies. A multielectrode electron tube is provided with the electrodes thereof respectively connected in a circuit arrangement for producing the desired mixing and amplifying effect.

Referring to the drawing in detail, a source of modulated high frequency energy is connected to the primary winding of a transformer 2 having a secondary winding connection to a potentiometer 3. The source I represents means for supplying modulation side band energy comprising one side band with the carrier frequency and other side band substantially eliminated, and may correspond to a power transmission network over which several programs are simultaneously Wired Radio, Inc., New York, N. Y., a corpora- 1936, Serial No. 86,129

transmitted as carrier eliminated modulation side band energy in discrete frequency ranges. After passing through a filter and amplifying circuits, this energy is directed to the input circuit of electron tube 4 having the control electrode thereof adjustably connected with the potentiometer 3, as shown. The tube 4 is of the triode type, although other forms of tubes may be employed, when desired. The anode circuit of the tube 4 includes a connection through a radio frequency choke 5 and thence to the positive B supply at terminal 6.

The carrier frequency source 8 is connected with the primary of the transformer 9. source 8 comprises the means for supplying the independent replacement carrier frequency corresponding to the frequency eliminated from the energy available at the source I. In accordance with the invention, means are provided for adjusting the phase relationship between the voltages of the source I and source 8. This carrier frequency may be impressed upon the transmission medium common to the source I or may be generated locally. The energy from the source 8 is directed through transformer 9 to a potentiometer I0 having an adjustable connection to the control electrode I I of a multi-electrode electron tube I2. The tube I-2 also includes a cathode, a screen electrode I3, a suppressor electrode I4, and an anode I5. The anode I5 is connected through the primary winding of a transformer I6 in an output circuit connection including the positive B supply terminal 6. The transformer I6 includes a secondary output connection with a load circuit II representing the utilization means, such as a program reproducing system.

In accordance with the invention, the suppressor electrode I4 is connected with the cathode of the tube I2 and is maintained at the same potential as the cathode. The screen electrode I 3 is connected in the anode circuit of the tube 4, as shown. Other circuit components not described are of an obvious nature and known to those skilled in the art.

In the operation of the system, the tubes 4 and I2 are provided with biasing potentials for optimum linear operating conditions as amplifiers. The potentiometers 3 and Ill are adjusted to provide an adjustable ratio or voltages from the sources I and 8. The modulation side band energy from the source I is then amplified by the tube 4 and directed to the screen electrode of the tube I2. Concomitantly, the carrier frequency from the source 8 is directed to the control electrode II of the tube I2. The two fre- The M quencies are then combined in a linear amplification to produce algebraic addition frequencies transmitted to the load circuit l'l. It is a feature of the invention that the circuit including the screen electrode I3 is substantially the correct impedance to serve as a load for the cascade stage of amplification represented by the tube 4. However, when necessary and desired, a transformer may be interposed in this circuit to produce matched impedances In operating the system, it may be desired to change the relation of the side band energy with respect to the replacement carrier frequency. To accomplish this, it is only necessary to adjust the potentiometers 3 and I0 to bring about a desired relation of energy levels. In accordance with the invention, the two inputs are completely isolated from each other and no reaction between the inputs is possible through the mixing system. Although a preferred form of the mixing amplifier has been disclosed, it will be recognized that various changes and modifications as well as equivalent forms can be produced without departing from the intended scope of the invention. Accordingly, no limitation of the invention is intended other than as imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A mixing amplifier comprising, a source of modulation side band energy with carrier frequency substantially eliminated, a source of carrier frequency energy corresponding in frequency to said eliminated carrier, a load circuit, a common combining circuit interconnecting said sources and said load circuit and including a multi-grid electron tube, the parameters of which are so chosen and adjusted with respect to the control grids thereof that said tube functions as a linear amplifier only, said circuit being interposed between one of said sources and said load and including a connection from one of the grids thereof with said one source, and means connecting the other of said sources with another of the grids of said tube for supplying energy thereto under control of the source connected with said second mentioned grid whereby the foregoing arrangement as a whole operates for producing currents in said load circuit corresponding respectively to said carrier frequency and said modulation side band to provide said modulation side band energy with a replaced carrier frequency.

a linear amplifier only, said combining circuit including a connection from one of the grids thereof with one of said sources, and another electron tube connected with the other of said sources, said second electron tube being coupled with another of the grids of said first mentioned tube for supplying amplified energy thereto under control of the source connected with said second tube whereby the foregoing arrangement as a Whole operates for producing amplified currents in said load circuit corresponding respectively to said carrier frequency and said modulation side band to provide said modulation side band energy with a replaced carrier frequency. EDMUND A. LAPORT.

said 

